Does degenerative disease of the lumbar spine cause arachnoiditis? A magnetic resonance study and review of the literature.

The magnetic resonance appearances in 165 patients with symptoms suggestive of degenerative lumbar spine disease were reviewed. The aim of the study was to evaluate the relationship between abnormalities of nerve root distribution and degenerative disease of the lumbar spine in the absence of other known risk factors for arachnoiditis. Central clumping of nerve roots was present in 16 patients (9.7%) and was associated with spinal stenosis at one of the affected levels in all (p < 0.001). Spinal stenosis was present in 44 patients giving an incidence of abnormal nerve root distribution of 36% in this group. Nerve root clumping occurred in association with pure spinal stenosis (10 cases), stenosis secondary to disc prolapse (four cases) and degenerative spondylolisthesis (two cases). Nerve root clumping was confined to one vertebral level in nine cases and extended over two to four levels in seven. In five of the latter spinal stenosis was present at multiple levels. The appearance of nerve root clumping described here may result entirely from mechanical apposition of nerve roots but is indistinguishable from the central pattern of nerve root adhesions which occurs in adhesive lumbar arachnoiditis. No abnormalities of nerve root distribution were seen in association with any indicator of degenerative disk disease in the absence of stenosis. We have been unable to demonstrate the previously reported relationship between lumbar disk degeneration and arachnoiditis and discuss this with a critical review of the literature. Abnormal central clumping of nerve roots as described in arachnoiditis may occur in association with spinal stenosis in the absence of other risk factors although the cause for this appearance remains unexplained. Arachnoiditis-like changes extending over more than one vertebral level are rare (7%) except in the presence of spinal stenosis at multiple levels (29%). Awareness of this appearance may avoid a possibly incorrect diagnosis of arachnoiditis in the presence of a treatable stenosis.